In the previous post, we discussed the concept of landslides, their causes, and different types of landslides. Landsliding is the movement of rock, earth, or debris down a sloped section of land. The study of landslides is important because they affect many types of engineering works, particularly highways and railways. Loose rock material ordinarily creeps downhill under the force of gravity. However on the sloping surface, in presence of water the creeping may become a fast-moving landslide. Thus the rate of movement of each material varies from very slow to very rapid. Therefore, the movement of the earth’s material is not confined only to landslides. If the movement is very slow and creepy, that is called an earthflow. We can classify the movement of earth material into two types, (i) Landslides and (ii) Earthflow. In this post, we are discussing the earthflow.
In earthflows, the unconsolidated material flows slowly downhill under the pull of gravity. The movement of the mass and well-defined slip surface, which is characteristic of landslides, does not occur. There are various types of earthflow, among them, the important types of earth-flows are as under:
(1). Soil Creeping: When the unconsolidated earth material moves slowly and continuously down the slope, it is called ”soil creep”. The rate of soil creep on a hillside depends mainly on temperature changes, amount of rainfall, angle of slope, types of soil, and nature of parent material. The soil creep is indicated by the presence of tilted fence posts, telegraph poles, curved tree trunks, broken and displaced retaining walls, lines of stone, accumulation in the soil, displacement of railway and highway alignments, and many other features.
(2). Rock Creep: When the well-jointed rock formations outcrop along hillslope, the large joint blocks are displaced by the process of rock creep. The movement consists mainly of slipping of joints blocks slowly in the downhill direction. The slates or thinly bedded sedimentary rocks, if exposed on a hillside, often bend downslope and may show reversal of true dip direction.
(3). Solifluctive creep: Solifluction is a type of creep, which takes place in regions of cold climate, where the ground freezes to a considerable depth. During the summer the ground thaws and the upper soil layer becomes saturated with water. This mass of water-saturated soil moves slowly downhill over the frozen material at greater deth.
(4). Mudflows: Mudflows differs from soil creep in the resect that they move more rapidly and usually follow old stream channels. Mudflows are produced in those steep mountainous areas where large amounts of loose earth materials are available and where abundant water is supplied by heavy rain or melting of snow. Mudflows have destroyed buildings, roads, and useful lands at many places in semi-arid regions.
- Relationship of geology with civil engineering
- Geology and Building-Stones
- Most common rocks used as building stones
- Geology of Dams
- Problems associated with a dam/failure of dams
- Geology of Reservoirs
- Geological investigation for construction of dams and reservoirs
- Tunnel Engineering
- Geological Survey of Tunnels
- Bridge Engineering
- Landslides and their causes